This invention relates to an apparatus for dispensing a liquid and more particularly to an apparatus having improved means for automatically preventing the passage of air after a predetermined amount of the liquid has been dispensed.
There are a number of operations where it is desired to deliver a discrete volume of a liquid without an attendant having to be present to terminate the flow of the liquid at the right time. For example, in the administration of parenteral solutions, particularly to pediatric patients, it is often critical that only a relatively small predetermined volume of the solution be given. It is a common practice in such cases to fill a metering container as part of an administration set with a known volume of the solution.
To avoid the possibility of air from entering the bloodstream of the patient, such metering containers have some form of valve or closure means at the bottom of the container which are intended to close the outlet at the bottom of the container when the solution level reaches this point. Typical of such valved metering devices are those disclosed in U.S. Pat. No. 3,216,419 wherein the valve comprises either a freely floating disc designed to close off the outlet when the level of the solution reaches the outlet or a floating disc anchored over the outlet at the bottom of the metering container by a flexible hinge. Experience has shown that valves of these types can not always be depended upon to close the outlet passage. The freely floating disc will sometimes stick to the side of the container and in the hinged variety, the disc will occasionally cant from the horizontal so as to prevent the disc from sealing the outlet.
Some metering containers have the floating disc retained about the outlet by a cage such as the devices in U.S. Pat. Nos. 3,625,211 and 3,774,603. These disc valves also fail to provide assurance of closing off the outlet since the cage structure tends to trap air bubbles, particularly when a liquid such as blood is being administered, so that the disc will not seal.
In the use of metered containers, the administration of a second or additional prescribed volume of solution is often desired, following the delivery of the first volume. When the additional solution is added to the metered container, the disc adheres to the bottom of the container and must be dislodged before the solution can flow to the patient. This is generally accomplished by squeezing a deformable member located below the metering chamber, such as a flexible drip chamber, which forces air up from the deformable member to unseat the disc and allow it to float. This dislodging operation is often difficult to achieve, particularly when the disc covers too large an area.
A disc valve for a blood transfusion apparatus is disclosed in U.S. Pat. No. 2,074,223, in which a disc is slidingly retained over an outlet by two posts near the periphery of the disc. The valve is designed so that the disc lifts off the outlet when blood flows upwardly against the disc but closes to prevent back flow of blood. There are no details to indicate whether such a valve would function in a metering container of the type described above.
Objects of the present invention are, therefore, to provide an apparatus for dispensing liquid which includes a floating disc valve capable of assuring closure to prevent the passage of air following delivery of liquid from the apparatus and to provide a disc valve in which the disc is easily dislodged from a sealing position prior to delivery of liquid.